Manifestation of intrinsic defects in optical properties of self-organizedopal photonic crystals

Self-organized synthetic opals possessing a face centered cubic (fcc) latti ce are promising fur fabrication of a three-dimensional photonic crystal wi th a full photonic band gap in the visible. The fundamental limiting factor of this method is the large concentration of lattice defects and, especial ly, planar stacking faults, which are intrinsic to self-assembling growth o f colloidal crystal. We have studied the influence of various types of defe cts on photonic band structure of synthetic opals by means of optical trans mission, reflection and diffraction along different crystallographic direct ions. We found that in carefully chosen samples the stacking probability cu can be as high as 0.8-0.9 revealing the strong preference of fee packing s equence over the hexagonal close-packed (hcp). It is shown that scattering on plane stacking faults located perpendicular to the direction of growth r esults in a strong anisotropy of diffraction pattern as well as in appearan ce of a pronounced doublet structure in transmission and reflection spectra taken from the directions other than the direction of growth. This doublet is a direct manifestation of the coexistence of two crystallographic phase s-pure fee and strongly faulted. As a result the inhomogeneously broadened stop-bands overlap over a considerable amount of phase space. The latter, h owever, does not mean the depletion of the photonic density of states since large disordering results in filling of the partial gaps with both localiz ed and extended states.